Refrigerant compressor having thermal overload protector



July 26, 1960 R. G. CARVER 2,946,203

REFRIGEIRANT COMPRESSOR HAVING THERMAL OVERLOAD PROTECTOR Filed March 9. 1959 ROBERT G. CARVER.

H 15 ATTORNEY INVENTOR- United States Patent REFRIGERANT COMPRESSOR HAVING THERMAL OVERLOAD PROTECTOR Robert G. Carver, Louisville, Ky., assignor to General Electric Company, a corporation of New York Filed Mar. 9, 1959, Ser. No. 797,953

1 Claim. (Cl. 62--2'30) The present invention relates to hermetically sealed refrigerant compressor Units and more particularly to an improved arrangement for providing thermal protection for the drive motor of such a unit.

In order to obtain maximum efiiciency for the size of motor used in refrigeration compressors, it is desirable to operate the motor at the maximum operable temperature which can safely be withstood by the insulation of the motor windings. In most of the present day refrigeration compressors which are mounted within a sealed hermetic case, the refrigerant gas itself is passed over the motor to cool the windings, thereby permitting the motor to be operated at a capacity which would, if the refrigerant cooling were not present, soon create suificient heat within the case to damage the insulation of the windings. In this type of compressor, if the flow of refrigerant over the motor ceases or is substantially reduced for one reason or another and the cooling of the motor by this refrigerant is no longer provided, or is greatly reduced, then the motor very quickly overheats to damage the insulation of the windings.

It is desirable, therefore, in the above type of compressors to provide a thermal protection device which stops the compressor when the temperature within the case approaches a degree which could damage the insulation of the windings. It has been found that those conditions which normally result in a reduction or complete stoppage of refrigerant flow through the system, such as compressor overload or locked rotor conditions, usually result in a greater amount of heat being generated from the rotor than from the remaining portions of the motor. In order to give adequate protection to the motor, it is desirable, therefore, that the heat dissipated by the rotor be immediately sensed by the thermal protecting device.

Accordingly, it is an object of the present invention to provide for a refrigerant compressor an improved thermal protective arrangement for interrupting the power to the motor whenever the heat generated by the motor cannot be safely dissipated by the refrigerant flowing thereover.

It is a more specific object of the present invention to provide for a refrigerant compressor an improved thermal protective arrangement adapted to quickly respond to the heat generated by the rotor of the motor whenever the motor is subjected to overload or locked rotor conditions resulting in a reduced flow of refrigerant gas through the compressor case.

Other objects and advantages of the present invention will become apparent as the following description proceeds and the features of novelty which characterize the invention will be pointed out with particularity in the claim annexed to and forming a part of this specification.

In carrying out the present invention there is provided a refrigeration motor-compressor unit mounted within a hermetic casing. The casing is adapted to receive refrigerant discharged from the compressor for cooling the motor. A thermal responsive switch means is provided in series with the electrical supply means for the motor for interrupting the current to the motor whenever the 2,946,203 Patented July 26, 1960 switch means senses a predetermined high temperature within the case. This thermal responsive switch means is disposed within a heat conducting metallic well mounted on the casing and extending into the sealed casing. Connected to the bottom portion of the well is a strap made of a heat conductive metal which extends to a position within the casing adjacent the rotor of the motor so that heat dissipated by the rotor is rapidly transmitted through the heat conductive strap to the metallic well and thereby to the thermal responsive switch in order to provide rapid response of the thermal switch to conditions resulting in more than the normal output of heat from the rotor.

For a better understanding of the invention reference may be had to the accompanying drawing in which:

Fig. l is an elevation view in cross-section of the preerred embodiment of the invention; and

Fig. 2 is a top view showing the thermal sensitive device with the heat conductive strap in dotted lines to indicate its relative position with respect to the thermal device and the rotor.

Referring now to the drawing, there is shown in Fig. 1 a compressor having a hermetic casing 2 in which is disposed a refrigerant compressor unit 3. The compressor unit 3 is rigidly mounted upon a main frame member 4 which supports the compressor within the hermetic casing 2. The main frame 4 also contains a journal bearing 6 which supports a drive shaft 7 leading to the compressor and arranged in a vertical position within the casing. Mounted directly above the main frame 4 for driving the shaft 7 and the compressor 3 within the hermetic casing 2 is a motor including a stator 9 and a rotor 10. The stator 9 compn'ses a laminated iron core 11 and the usual field coils 12 wound thereon. The rotor is normally pressed or shrunk onto the shaft 7, although it could be mounted by any of the methods well known in the art, and fits within the interior diameter of the stator core, leaving a small air gap 13 between the outer surface of the rotor and the inner surface of the stator. The rotor 10 is provided with end rings 14 which connect the opposite ends of the electrical conductors or conductive bars (not shown) extending through slots in the rotor. Power is supplied to the motor through power supply lines 18 and 19 which connect through the terminal cover 21 to the motor leads 22 within the casing 2.

Low pressure refrigerant gas from the refrigeration system enters the compressor unit 3 through the suction line 8 wherein the gas is compressed and discharged into the casing 2 through the port 16 provided in the main frame 4. The compressed refrigerant gas then flows upwardly through coo-ling holes (not shown) provided in the stator and through the air gap 13 between the rotor and stator to cool the motor. After removing some of the heat from the motor the compressed gas is discharged back into the refrigerating system through the discharge tube 17 in the top of the compressor. The inlet to the discharge tube 17 is disposed in the top of the compressor just above the center of the rotor so that the gas entering the tube is first subjected to a swirling or vortex action as it passes the upper portion of the rotor and this promotes the separation of oil particles from the refrigerant gas before it discharges from the case. Sometimes it is desirable to pass the compressed refrigerant gas directly from the compressor unit 3 into a de-superheater coil before the gas is discharged into the case to cool the motor. In such a case the superheat removal coil comprises a few tubes positioned on the outside of the easing into which the gas discharging from the compressor unit 3' is directed. The compressed gas is partially cooled as it flows through this coil and is then discharged back into the casing to cool the motor. Use of a de-superheater coil provides a greater cooling capacity in the gas flowing through the motor thereby permitting the motor to be operated at a higher capacity. Although the illustrated embodiment is shown without a superheat removal coil, it will be understood that the invention may be applied to a compressor using such a coil.

In order to provide thermal protection for the motor within the case, there is provided a thermal protection device 23 connected in series with the terminals 21 of the terminal cover and provided with a thermal responsive switch (not shown) which breaks the current to the terminal box 21 whenever a predetermined temperature is sensed by the protector. This thermal protector may be any of the well known types of thermal protection devices now on the market which are adapted to open a switch upon sensing a predetermined temperature. The thermal protective device is seated in a metallic cup 2 which is mounted in the top of the casing. This cup or well 24 is made of a thermally conductive metal and extends downwardly a short distance into the casing so that it is surrounded by the refrigerant gas in the top of the casing. Because the metallic cup is a good heat conductor, the temperature normally sensed by the thermal protector is substantially the same as that of the gas surrounding the well 24. The rim of the well is sealed around its periphery to the top of the casing so that none of the refrigerant gas can escape at this point from the casing. Arranging the thermal protective device 23 within the metallic well 24 in this manner permits the device to be in fairly close thermal contact with the gases within the casing while still permitting access to the device from the outside.

As may be seen from the drawings, the well 24 and the thermal protective device are oif-set from the center of the top of the case toward the outer periphery thereof. This is done for two purposes. First, to permit the discharge tube 17 to enter the case at the center thereof over the top of the rotor in order to take advantage of the oil separation action of the swirling gas adjacent the top of the rotor. Second, by placing the thermal protector toward the periphery of the case, it is in a position to sense heat dissipated by the motor windings.

During all normal operations of the compressor refrigerant gas flowing upward through the motor components is heated by these components and transmits heat proportional to the temperature of these components through the metal well 24 to the thermal protector 23. As long as gas is flowing through the case, the temperature of this gas, which is a function of the temperature of the motor, is immediately sensed by the thermal protector. However, under certain operating conditions when there is insufficient refrigerant gas flowing through the case or when it completely stops flowing, there is a substantial delay before the motor temperatures are felt by the thermal protector. Gas flow through the case is sometimes afiected during overload conditions and completely stops whenever locked rotor conditions occur. It has been found that, the amount of heat dissipated by the rotor during locked rotor or overload conditions is very great and that, under these conditions, there is danger of damaging the insulation of the windings in the area adjacent the end rings of the rotor before this heat is sensed by the thermal protector. That is, because of the reduced refrigerant flow there is not only a lack of cooling of the area surrounding the upper end ring 14, but the heat dissipated by the rotor is not carried by the refrigerant gas to the thermal protector.

In order to give adequate protection to the windings of the motor whenever more than the normal amount of heat is dissipated by the rotor, the present invention provides a heat conducting arm or strap 26 which is attached to the bottom 27 of the metal well 24 and which extends downwardly into the casing adjacent the upper end ring 14 of the motor. This strap 26 may be made of copper or any other good heat conducting material and is welded or brazed to the bottom of the well 24 in order to provide rapid transfer of heat to the well from the strap and thence to the thermal protection device 23 seated within the well. By arranging the lower end 23 of the heat conducting strap 26 adjacent the upper part of the rotor, and the upper end ring 14, the strap is very quickly heated by the heat generated by the rotor, and immediately conducts this heat upwardly along the strap to the bottom of the well 24 and to the thermal sensing device 23. When there is little or no gas flow through the case, the strap 26, which is a much better heat condutcor than the gas, makes certain that whenever more than the normal amount of heat is dissipated by the rotor, it will be very quickly transmitted to the thermal protector. Thus, whenever the rotor operates above a predetermined temperature and the gas flow is insufficient to cool the rotor and transfer this heat away from the rotor, then this heat is immediately carried, via the strap 26, to the thermal protector 23 which interrupts the current flowing to the compressor. After the heat sensed by the thermal sensitive device 23 has somewhat subsided, the device again completes the circuit to the compressor through the lines 18 and i9 and power is again supplied to the compressor until such time as the heat within the casing again causes the thermal sensitive device to interrupt the current.

By the present invention there has been provided an improved thermal protector arrangement for interrupting the electrical power to the compressor motor whenever the heat generated by the motor cannot be safely dissipated by the refrigerant flowing over the motor. Moreover, this arrangement immediately responds to the heat generated by the rotor whenever this heat is not carried away by refrigerant gas, such as during periods of reduced refrigerant flow through the case caused by locked rotor or heavy compressor overload conditions.

While in accordance with the patent statutes there has been described what at present is considered to be the preferred embodiment of the invention, it will be understood by those skilled in the art that various changes and modifications may be made therein without departing from the invention and it is, therefore, the aim of the appended claim to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

In a compressor for a refrigerating system, the combination comprising a sealed casing, a compressor unit disposed within the lower portion of said casing, an electric motor including a rotor and a stator disposed in said casing above said compressor for driving said compressor unit, means for conducting low pressure refrigerant gas from the refrigerating system into said compressor unit, means for discharging compressed refrigerant gas from said compresser unit into said casing, a discharge tube for conducting compressed refrigerant gas from said casing back into said refrigerating system, said discharge tube having an inlet opening in the upper portions of said casing directly over said rotor so that refrigerant gas being discharged by said compressor unit is forced to flow upwardly over said motor to cool said motor prior to being discharged from said casing, means for supplying an electrical current to said motor, thermal responsive switch means for interrupting the electrical current to said motor when said thermal responsive switch means senses a predetermined high temperature, a heat conductive metallic well mounted in the upper portion of said casing and extending downwardly into said casing adjacent the windings of said stator, said thermal responsive switch means being disposed in said metallic well so that the heat of said refrigerant gas surrounding said well is transferred through said well to said thermal responsive switch means, and a heat conductive copper arm bonded to the base of said metallic well, said copper arm extending inwardly toward the central portion of said casing and having an end portion extending downwardly adjacent said rotor so that heat dissipated 5 by said rotor which is not carried away by said refrigerant gas is transmitted through said copper arm to said thermal responsive switch means to promote rapid response of said thermal responsive switch to heat dissipated by said rotor when the flow of refrigerant gas through said case 5 is reduced or stopped.

6 References Cited in the file of this patent UNITED STATES PATENTS 2,089,249 Bruns Aug. 10, 1937 2,159,592 Kaliseher May 23, 1939 2,523,059 Richert Sept. 10, 1950 

